LITMIR.BIZ

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amount of action exercised by our earth upon such a ball.

      No hypothesis failing to embrace each of these six requirements deserves consideration ; and any hypothesis fully covering them all, might be expected to account equally for the quite incomparable actions of elasticity, magnetism, affinity, and cohesion, before being entitled lo acceptance as a just or comprehensive theory of molecular force.

      As the projectors of kinetic systems of gravitation have almost invariably quite ignored the fourth of the above conditions, it is worth while here to dwell somewhat upon this point. Swift as the earth's orbital motion is, (upward of 18 miles in one second,) the velocity of light is about ten thousand times greater, being 185,000 miles per second. And yet the composition of these two velocities gives .a displacement or '.'aberration" of the heavenly bodies, as seen from our earth, of about 20" of angle for the observed direction of the visual ray. A luminous impulse emanating from the sun requires about 8¼ minutes to reach the earth. Were the gravitative influence supposed to be so much swifter than light as to require but a single minute to pass through this distance, there would still be a corresponding gravity "aberration" of 2.4" of angle. The effect of this slight obliquity of traction would be an acceleration of the earth's orbital velocity which would become measurable in a single year.

This is a subject which has been very fully and carefully investigated by astronomers; and the illustrious Laplace, when he found an unexplained minute acceleration in the moon's orbit, threw out the suggestion that if the velocity of transmission of gravitation did not exceed eight million times that of light, it would satisfactorily explain the lunar anomaly. It is scarcely necessary to say that when he subsequently discovered the secular diminution of eccentricity in the earth's orbit, at present continuing, (though slowly reaching its minimum,^[1]) he recognized the true cause of the moon's irregularity, which no longer permitted even the unimaginable limit of possible velocity he had provisionally assigned for gravitative action.

Arago has remarked : " Now if we apply to the perturbation the maximum value which the observations allow, when they have been corrected for the known acceleration due to the variation of the eccentricity of the terrestrial orbit, we find the velocity of the attractive force to amount to fifty millions of times the velocity of light."^[2] [213]

If it is possible to represent in such terms the lowest assignable limit of transition, it is because we are furnished with a test of planetary movement of most marvelous delicacy in the record of eclipses occurring at a particular locality 2,000 years ago ;—fixing the relation of annual revolution to diurnal rotation with an almost absolute precision. Sir John Herschel remarks: "From such comparisons Laplace has concluded that the sidereal day has not changed by so much as one-hundredth of a second since the time of Hipparchus!"^[3] This implies the absence of even an infinitesimal "aberration" of the gravity radiant, or the negation of any assignable interval for its full and complete action. Hence the fourth category above stated.

      The same consideration serves to show that the energy of gravity has undergone no abatement or change during the lapse of two thousand years. Hence the sixth category.

      It is but just however, to notice here that a minute outstanding anomaly of the moon, detected in recent years, and still unexplained, detracts somewhat from the accuracy of the above infinitesimal measure ; though it does not impair the value of the general argument. Every investigation, every calculation, of the astronomer, assumes the action of gravity to be for all distances—absolutely instantaneous.

      1 ↑ The minimum eccentricity will be reached in about one '"precession" period, or 25,000 years hence.

      2 ↑ Popular Astronomy, book xxiii, chap. 27, vol. ii, p. 469 of the English edition. To represent the real meaning of this velocity, it may be put into the equivalent form, that if gravity occupied the one hundred -thousandth of a second in passing from the sun to the earth, it would be detected. Or, the time required to reach us from the nearest star (distant in light-travel about three years) would not exceed two seconds.

      3 ↑ Outlines of Astronomy, chap, xviii, sec. 908.

      Villemot, 1707

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      Philippe Villemot, a French doctor of theology, and a distinguished mathematician, published at Lyons in 1707 an astronomical treatise, entitled Nouveau Système, ou Nouvelle Explication du Mouvement des Planetes, in which, referring the movements of the planets to Cartesiab vortices, he announced the theory that their gravitation is occasioned by a difference of pressure, on their outer and inner faces, of the fluid constituting the solar vortex, owing to an increase of its density outward from the sun. The general conception is obviously somewhat similar to the speculation cursorily hazarded by Newton in 1679, and again recurred to by him (though only transiently) in 1717, or ten years later than the above publication by Villemot.

      The details of this system cannot here be given, from want of access to his work. The Nouveau Système, however, appears to have been very favorably received by the author's contemporaries.

      Bernouilli, 1734

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It is now nearly a century and a half since the elder John Bernouilli, of Switzerland, the illustrious mathematician, (professor at the universities of Groningen and afterward of Basel,) imagined a method of accounting for the action of gravitation by centripetal impacts from without. Still retaining his early prepossessions in favor of the philosophy of Descartes, he devised a very curious combination of aetherial vortices and Newtonian emissions. This eclectic hypothesis was promulgated [214] in a competitive memoir on the cause of " The Mutual Inclination of the Planetary Orbits," which obtained the prize of the French Academy of Sciences in 1734. This treatise is divided into four parts, the first three of which are occupied with his exposition of the cause of gravitation, and the fourth with the main question proposed.^[1]

Referring to the respective systems of Descartes and Newton, Bernouilli finds in each "insurmountable difficulties," hence " a just mean between the two appears the safer course. … The gravitation of the planets toward the center of the sun, and the weight of bodies toward the center of the earth, are not caused either by the attraction of Newton, or by the rotary force of the vortex medium of Descartes, but by the immediate impulsion of a substance which under the form of what I call a ' central torrent,' is continually thrown from the whole circumference of the vortex to its center, and consequently impresses on all bodies encountered by it in its path the same tendency toward the center of the vortex. … And all that Newton has derived from his ' attractions' are by my theory, derived from the impulsions of the central torrent."^[2]

      "According to my system, two kinds of matter are conceived as occupying planetary space, and also two principal movements in the celestial vortex. One of these materials I conceive as perfectly fluid, or I would say, actually divisible without limit; that is, it is not composed of elementary corpuscles, as ordinary fluids are conceived, which according, the number and size of their constituent particles, present more or less sensible resistance to bodies moving in them, but being perfectly uniform and without structure, is also without resistance." This matter is called the primal element ; which was employed by the Creator in forming the corpuscles of sensible matter, definite small portions being compacted together into the coherent molecules of matter of the second element.

" Matter of the primal element, being perfectly fluid without coherence, presents no resistance to bodies moving within it ; for the resistance of fluids comes only from the inertia of the molecules of which they are composed."^[3] This primal element, being without constituent parts and without inertia, is as the author states, the

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